1. Field of the Invention
This invention generally relates to integrated electronic circuitry and, more particularly, to a circuit for the selection of power supply sources.
2. Description of the Related Art
Portable devices typically use an internal battery to supply power. The most important figure of merit of a battery in today's power hungry device landscape is the battery lifetime (for a non-re-chargeable battery) or the time between two chargings (for a re-chargeable battery). This time is inversely proportional to the amount of power drawn from it. So, in order to increase battery lifetime, the use of external supply to source power, whenever available, is desired.
It would be advantageous if the functions of power supply source switching could be simplified enough to be implemented as a feature of a monolithic device circuit.